Lin-tong Yang’s research while affiliated with Guangdong Ocean University and other places

Hypoxia is a lack of required oxygen to meet the metabolic demands of living organisms. Cellular hypoxia occurs when the molecular oxygen, essential to maintain sufficient adenosine triphosphate (ATP) levels for normal physiological function, surpasses the vascular supply. Tissue hypoxia can arise during a range of diseases. As molecular oxygen is a crucial metabolic energy source for all living organisms, animals manage the intracellular oxygen levels to sustain homeostasis, with the upregulation of genes that improve tissue perfusion and anaerobic ATP creation via glycolysis. This is facilitated by the hypoxia-inducible factors (HIFs). Hypoxia-inducible factor 1α (hif-1a) is the core regulator of the hypoxia response and plays a crucial role in the cellular/molecular response to hypoxic stress by regulating the transcription of target genes. In the present study, hif-1a cDNA was identified and cloned from cobia (Rachycentron canadum), using rapid amplification of cDNA ends (RACE). The hif-1a and downstream mRNA expression levels in various tissues were then determined. The full length of hif-1a cDNA is 3642 bp, with a 2292 bp open reading frame (ORF), a 5′ non-coding region (5′-UTR) of 293 bp, 3′ non-coding region (3′-UTR) of 1057 bp, and encoding 764 amino acids. The encoded protein contains the basic helix-loop-helix domain (amino acid 22–77), PER-Arnt-SIM domain (amino acid 88–154 and 230–296), and the PAS-associated C-terminal domain (amino acid 302–345). hif-1a mRNA expression was detected in nine tissues, with the highest expression observed in the liver, and the lowest expression in the intestine and spleen. hif-1a, erythropoietin (epo), and vascular endothelial growth factor (vegf) gene expressions were analyzed in the gill, intestine, liver, and muscle under hypoxic stress. In the gills, hif-1a expression was significantly increased at all hypoxia time points as well as in the liver. Erythropoietin (epo) and vascular endothelial growth factor (vegf) showed similar trends, with a significant decrease followed by a significant increase. In the muscle, the expression of all three genes was higher than the control group after hypoxic stress. These results indicate that the expression patterns of hif-1a and related genes after hypoxic stress are tissue-specific and play an essential role in cobia’s response to hypoxia.

In this study, juvenile cobia fish (Rachycentron canadum) (body weight: 50.44 ± 2.78 g) were used as a study object to investigate the effects of hypoxia stress (dissolved oxygen: 3.15 ± 0.21 mg/L) on the activities of their digestive enzymes, intestinal morphology and relative expression of tight junction proteins coding genes. Under the experimental conditions, the juvenile cobia were given 28 days of hypoxia stress. The results showed that the activities of digestive enzymes in the intestines of the hypoxia stress group decreased. In addition, the amylase and lipase activities decreased significantly (p < 0.05), and the trypsin activity in the hypoxia stress group compared to that in the control group. The morphology and structure of the intestine also showed significant changes. Under the microscopic observation, the mucosal fold height and muscle thickness of the intestine showed a significant decrease (p < 0.05); also, the villi's width showed a significant decrease (p < 0.05) in the hypoxia stress group as compared to that in the control group. The observation under a transmission electron microscope showed that the microvilli of juvenile cobia in the hypoxia stress group were irregularly arranged, atrophied and fallen off compared to the control group. Furthermore, there were gaps in the tight junction. In addition, the boundary between cells was unclear. The relative expression of intestinal tight junction proteins coding genes was down‐regulated to varying degrees. The mRNA expressions of ZO‐1 and claudin‐4 were significantly down‐regulated (p < 0.05) and ZO‐2 and occludin in the hypoxia stress group compared to those in the control group. These results indicated that hypoxia stress could inhibit the activities of intestinal digestive enzymes, damage intestinal morphology and decrease the expression of tight junction proteins coding genes in cobia. The present study provided a scientific foundation for evaluating the multifaceted impacts of hypoxia stress on fish species, such as cobia.